Patent application title: BANANA PLUG

Abstract:

The invention relates to an electrical plug connector, in particular a
banana plug, having a base body (2) and having a contact pin (3) which is
arranged on the front face of the base body (2), with the base body (2)
having a connecting cage (4) for holding a connecting cable and for
making an electrically conductive connection to the contact pin (3). The
invention is based on the object of providing a better plug connector.
The plug connector is intended to have good characteristics for
transmission of audio signals. A further aim is that it should be
possible to produce the plug connector at low cost. In order to achieve
this object, the invention proposes that the contact pin (3) comprise two
or more contact segments (5) and be in the form of a metallic stamped and
bent part, with at least one of the contact segments (5) being at least
partially embedded in the base body (2), which is composed of plastic,
and extending into the interior of the connecting cage (4).

Claims:

1. Electrical plug connector, particularly a banana plug, having a base
body (2) and a contact pin (3) disposed on the front side of the base
body (2), whereby the base body (2) has a connecting cage (4) for
accommodating a connecting cable and for producing an electrically
conductive connection with the contact pin (3),whereinthe contact pin (3)
comprises two or more contact segments (5) and is configured as a
metallic stamped and bent part, whereby at least one of the contact
segments (5) is at least partially embedded in the base body (2), which
consists of plastic, and extends into the interior of the connecting cage
(4).

2. Electrical plug connector according to claim 1, wherein the contact pin
(3) consists of a material having high conductivity, whereby the specific
conductivity of the material amounts to at least 5010.sup.6 S/m,
preferably at least 5510.sup.6 S/m, most preferably at least 6010.sup.6
S/m.

3. Electrical plug connector according to claim 1, wherein the material of
the contact pin (3) is copper or silver.

4. Electrical plug connector according to claim 1, wherein the contact pin
(3) consists of at least two contact segments (5) that are connected with
one another at the front end (6) of the contact pin (3), whereby one of
the contact segments (5) is extended in length as compared with the other
contact segments (5), and has a connecting surface (7) for the connecting
cable on its end side.

5. Electrical plug connector according to claim 4, wherein the extended
contact segment (5) lies against the inside wall in the interior of the
connecting cage (4), whereby the connecting cable can be pressed against
the connecting surface (7) by means of at least one clamping screw (8).

6. Electrical plug connector according to claim 5, wherein the at least
one clamping screw (8) is guided in a metallic threaded plate (9), which
is embedded into the base body (2) in the region of the connecting cage
(4).

7. Electrical plug connector according to claim 5, wherein the connecting
cage (4) has an introduction opening for the connecting cable, whereby
the at least one clamping screw (8) can be screwed in transverse to the
introduction direction of the connecting cable.

8. Electrical plug connector according to claim 1, further comprising a
spreader pin (11a, 11b) that can be screwed into the base body (2), from
its back, whereby the spreader pin (11a, 11b) extends into the contact
pin (3) with its front end, which narrows conically toward the front, so
that the contact pin can be radially widened by screwing the spreader pin
(11a, 11b) in.

9. Electrical plug connector according to claim 8, wherein the spreader
pin comprises a metallic spindle (11a) and a handle part (11b) made of
plastic, whereby the spindle (11a) is embedded in the plastic material of
the handle part (11b) and whereby the handle part (11b) has an outside
thread (12) that is guided in an inside thread of the base body (2).

10. Electrical plug connector according to claim 8, further comprising a
slit spreader sleeve (13) made of spring-elastic material, disposed in
the interior of the contact pin (3), whereby the front end of the
spreader pin (11a, 11b), which narrows conically, moves into the spreader
sleeve (13) when the pin is screwed in, and widens the sleeve when this
is done.

11. Electrical plug connector according to claim 8, further comprising a
latch (14) that can be releasably connected with the base body (2),
whereby the latch (14) has a locking projection (15) that engages into a
circumferential groove (16) of the spreader pin (11a, 11b) and thus
prevents the spreader pin (11a, 11b) from being completely screwed out of
the base body (2).

12. Electrical plug connector according to claim 1, further comprising an
elastically deformable spreader body (19) that stands under radial bias
in the interior of the contact pin (3), which body widens the contact pin
(3) radially and elastically.

13. Electrical plug connector according to claim 1, further comprising an
adaptation sleeve (10) that can be inserted into the introduction opening
of the connecting cage (4), whereby the inside diameter of the adaptation
sleeve (10) essentially corresponds to the outside diameter of the
connecting cable.

14. Electrical plug connector according to claim 13, wherein the
adaptation sleeve (10) has a passage bore for at least one clamping screw
(8).

15. Electrical plug connector according to claim 1, wherein the base body
(2) has a section angled transverse to its longitudinal axis, which forms
the connecting cage (4).

16. Electrical plug connector according to claim 15, wherein the base body
(2) is configured in multiple parts, specifically in such a manner that
the section that forms the connecting cage (4) can be removed.

17. Electrical plug connector according to claim 1, wherein a security pin
(18) that runs parallel to the contact pin (3) is formed onto the base
body (2), which pin prevents the contact pin (3) from being inserted into
a power outlet.

Description:

[0001]The invention relates to an electrical plug connector, particularly
a banana plug, having a base body and a contact pin disposed on the front
side of the base body, whereby the base body has a connecting cage for
accommodating a connecting cable and for producing an electrically
conductive connection with the contact pin.

[0002]A so-called banana plug is a common electrical plug connector. Its
principle was developed in electrical laboratories at the beginning of
the 20th century, as a replacement for complicated screw/squeeze
connections in test wiring setups that had to be changed frequently.
Because of its contact principle and its standard dimensions, it is
particularly suitable for use in releasable loudspeaker connections with
non-extreme cable cross-sections in high-quality hi-fi systems.

[0003]For use in the hi-fi sector, so-called angled banana plugs are known
from the state of the art, for example from DE 295 04 240 U1. These are
characterized by their angled construction, which is particularly
advantageous with regard to handling. In the case of angled banana plugs,
the base body of the plug has a section that is angled as compared with
its longitudinal axis, which section forms the connecting cage for
accommodating the connecting cable. The connecting cage comprises a
cavity having a contact element disposed within it, for producing an
electrical connection between the connecting cable and the contact pin.
The connecting cable can be introduced into the connecting cage through
an introduction opening. The connecting cable can be fixed in place in
the interior of the connecting cage, in most cases by way of suitable
clamping screws, whereby the connecting cable is pressed against the
contact element. Angled banana plugs of the aforementioned type are
furthermore configured so that they can be braced. This means that the
contact pin can be widened radially. The contact pin can therefore be
braced in the related jack, whereby the contact surfaces of the contact
pin are pressed against the contact surfaces of a corresponding plug jack
under high contact pressure. As a result, a particularly low transition
resistance and thus an excellent electrical connection are obtained.

[0004]In the case of the angled banana plug previously known from DE 295
04 240 U1, as mentioned above, the base body, having the angled
connecting cage and the contact pin, consists of a one-piece, homogeneous
material piece. This results in various disadvantages.

[0005]In the case of the known angled banana plug, the base body,
including the angled connecting cage and the contact pin, is formed from
a correspondingly shaped one-piece hot-pressed part made of brass,
bronze, red brass, or the like. The cavity of the connecting cage as well
as threads and bores are produced by means of cutting machining. The use
of better conductive materials, such as pure copper or pure silver, for
example, is not absolutely necessary for reasons of electrical
resistance, namely because of the large cross-sections of the one-piece
base body in the known plug design. For reasons of processing technology,
the use of better conductive materials is not possible, since pure copper
or pure silver, for example are not suitable for cutting machining. For
cost reasons, the use of materials such as copper or silver for the base
body of an angled banana plug of a conventional design would actually be
nonsensical. Nevertheless, the use of materials having higher
conductivity would open up improvement potentials for banana plugs used
in the hi-fi sector. This is because the coupling and conduction
capacitances that are formed by the voluminous base body of the
conventional construction could be reduced with such materials,
specifically by means of the possibility of the significant reduction in
the metallic conductive masses. At the same time, a reduction in the
active and passive EMI problem locations of the conventional plug design
would be achieved in this way. Furthermore, a reduced conductive volume
offers no or at least less room for the formation of eddy currents, whose
interference with the signal currents leads to significant impairment of
the signal reproduction.

[0006]Against this background, it is the task of the invention to make
available an improved electrical plug connector. A banana plug is
supposed to be created, which allows transmission of audio signals at
high sound quality. At the same time, it is supposed to be possible to
produce the plug in cost-advantageous manner.

[0007]This task is accomplished by the invention, proceeding from an
electrical plug connector of the type indicated initially, in that the
contact pin comprises two or more contact segments and is configured as a
metallic stamped and bent part, whereby at least one of the contact
segments is at least partially embedded in the base body, which consists
of plastic, and extends into the interior of the connecting cage.

[0008]According to the invention, the contact pin of the banana plug is
configured to be segmented. The contact pin is produced from metallic
flat material, which is given the shape required for functioning by means
of bending technology deformation. A material having high conductivity,
such as copper or silver, for example, can be used for the contact pin.
So that the specific conductivity of the material of the contact pin is
adapted to the conductivity of the connecting cables usually used in the
hi-fi sector, the specific conductivity of the material should amount to
at least 50×106 S/m, preferably at least 55×106
S/m, most preferably at least 60×106 S/m. Copper and silver
can be used without problems, since no cutting machining of the material
is required.

[0009]At least one of the contact segments of the contact pin is at least
partially embedded into the base body, which consists of plastic. The
base body therefore consists essentially of plastic in the case of the
plug connector according to the invention. The plastic material forms the
supporting structure of the plug connector. The at least one contact
segment can be embedded in the material of the base body by means of
injection-molding the body around it. The plug connector according to the
invention therefore has a lower metal proportion as compared with
conventional angled banana plugs. The disadvantages described above,
which result from the configuration of the base body as a solid metal
part, are therefore avoided by the invention. The plug connector
according to the invention is optimized not only with regard to its
electrical properties in signal transmission, but also with regard to the
production costs.

[0010]The electrical plug connector according to the invention can be used
like a conventional angled banana plug. The connection is made in usual
manner, in that the corresponding connecting cable is electrically
connected with the contact pin in the connecting cage. For this purpose,
it is provided, according to the invention, that the at least one contact
segment, which is embedded in the base body that consists of plastic,
extends into the interior of the connecting cage. There, the electrical
connection with the connecting cable is produced.

[0011]According to a practical further development of the plug according
to the invention, the contact pin consists of at least two contact
segments that are connected with one another at the front end of the
contact pin, whereby one of the contact segments is extended in length as
compared with the other contact segments, and has a connecting surface
for the connecting cable on its end side. In this embodiment, the
metallic stamped part of the contact pin--seen in the developed view--has
a star shape. Proceeding from this shape, the shape required for
functioning of the contact pin can be produced using only a few bending
technology deformation steps. At the same time, the connection of the
segments at the tip of the contact pin ensures good mechanical stability.
The plug can be plugged into a corresponding jack multiple times, without
any problems, without any damage to the contact pin having to be feared,
for example due to bending of the contact segments. The end of one of the
contact segments is configured as a connecting surface for the connecting
cable. The corresponding contact segment is embedded in the plastic
material of the base body, whereby the connecting surface is situated at
the end of the contact segment, in the interior of the connecting cage,
so that an electrical connection with the connecting cable can be
produced there.

[0012]It is practical if the extended contact segment lies against the
inside wall in the interior of the connecting cage, whereby the
connecting cable can be pressed against the connecting surface by means
of at least one clamping screw. In this embodiment, the contact segment
supports itself on the inside wall of the connecting cage, in the region
of the connecting surface for the connecting cable. Thus, the connecting
surface of the contact pin can be used to produce a clamping connection
with the connecting cable. The clamping forces that occur are absorbed by
the base body, which consists of plastic, on which the contact segment in
question supports itself.

[0013]In order to guarantee sufficient mechanical stability, the at least
one clamping screw can be guided in a metallic thread plate that is
embedded into the base body in the region of the connecting cage. In the
production of a clamping connection with the connecting cable,
significant forces might occur, under some circumstances. These forces
could put too much stress on a thread formed in the plastic material of
the base body. In order to minimize the risk of damage to the plug
connector in cases in which the clamping screw is severely
over-tightened, it is practical to use a metallic threaded plate in which
the thread for the clamping screw is formed. Only a minimally increased
metal proportion of the overall plug design results from the threaded
plate. The properties of the plug in the transmission of audio signals
are not measurably influenced by this.

[0014]In conventional manner, in the plug connector according to the
invention, the connecting cage can have an introduction opening for the
connecting cable, whereby the at least one clamping screw stands
transverse to the introduction direction of the connecting cable. This
results in practical handling of the plug connector according to the
invention, which handling corresponds to that of conventional angled
banana plugs.

[0015]According to a practical further development, the electrical plug
connector according to the invention has a spreader pin that can be
screwed into the base body, from its back, whereby the spreader pin
extends into the contact pin with its front end, which narrows conically
toward the front, so that the contact pin can be radially widened by
screwing the spreader pin in. As a result of the radial widening, the
outer contact surface of the contact pin can be pressed against the inner
contact surface of a corresponding jack, in order to produce a
particularly good electrical connection and to fix the plug connector in
place in the jack. The spreader pin is disposed coaxial to the contact
pin. For bracing, the spreader pin is screwed into the base body, whereby
the conically narrowing end of the spreader pin moves forward, into the
contact pin. In this connection, the contact segments of the contact pin
are pushed outward.

[0016]It is practical if the spreader pin comprises a metallic spindle and
a handle part made of plastic, whereby the spindle is embedded in the
plastic material of the handle part and whereby the handle part has an
outside thread that is guided in an inside thread of the base body. In
this embodiment, only the spindle consists of metal, while the handle
part consists of plastic. The metallic spindle ensures that the
mechanical forces that occur when the plug is braced in a related jack
are reliably transferred. Because of the production of the spindle from
metal, less wear is furthermore guaranteed, even if the plug connector is
frequently released and braced again. The production of the handle part
of the spreader pin from plastic brings about the result that the metal
proportion in total is kept low.

[0017]According to a practical further development of the braceable plug
connector according to the invention, a slit spreader sleeve made of
spring-elastic material is disposed in the interior of the contact pin,
whereby the front end of the spreader pin, which narrows conically, moves
into the spreader sleeve when the pin is screwed in, and widens the
sleeve when this is done. The inside diameter of the spreader sleeve is
less, in the unbraced state, than the outside diameter of the spindle of
the spreader pin. When the spindle moves into the spreader sleeve, the
latter is widened. The spreader sleeve ensures that the radial forces
that occur during bracing are uniformly transferred to the contact
segments of the contact pin over the entire surface of the spreader
sleeve, so that the outer contact surface of the contact pin is uniformly
pressed against the inner contact surface of a related jack. In the case
of the plug connector according to the invention, the contact pin, as
explained above, consists of a flat metallic material, for example of
copper or silver. The flat contact segments have little elasticity. The
elastic spreader sleeve ensures that permanent plastic deformations of
the contact pin do not occur during bracing of the plug. Furthermore, the
spreader sleeve prevents direct mechanical contact of the front end of
the spreader pin with the inside surface of the contact pin. As a result,
abrasion and wear of and also damage to the comparatively sensitive
contact segments during bracing are prevented.

[0018]According to another practical embodiment, the electrical plug
connector according to the invention has a latch that can be releasably
connected with the base body, whereby the latch has a locking projection
that engages into a circumferential groove of the spreader pin and thus
prevents the spreader pin from being completely screwed out of the base
body. The latch ensures that the spreader pin can only be screwed out of
the base body as far as is necessary to release the bracing. The spreader
pin, which is disposed in the interior of the contact pin, ensures
stabilization of the contact pin. Screwing the spreader pin out
completely could lead to destabilization of the contact pin, so that the
risk of damage to the contact pin would be present when it is inserted
into a jack. Furthermore, loss of the spreader pin is also effectively
prevented by the latch.

[0019]An alternative possibility for producing a good electrical
connection by means of pressing the outer contact surface of the contact
pin against the inner contact surface of the corresponding jack by means
of radial widening of the contact pin consists in disposing an
elastically deformable spreader body that stands under radial bias in the
interior of the contact pin, which body widens the contact pin radially
and elastically. This variant is more cost-advantageous, since the
spreader pin mentioned above is eliminated. The spreader body stabilizes
the contact pin sufficiently, so that no damage occurs when it is
inserted into the jack. At the same time, insertion of the plug into the
jack does not cause any problems, since the spreader body ensures that
the outside diameter of the contact pin automatically adapts precisely to
the inside diameter of the jack, without overly large friction forces
occurring.

[0020]Furthermore, an embodiment of the plug connector according to the
invention is practical, in which an adaptation sleeve that can be
inserted into the introduction opening of the connecting cage is
provided, whereby the inside diameter of the adaptation sleeve
essentially corresponds to the outside diameter of the connecting cable.
The adaptation sleeve serves essentially for strain relief. Depending on
the diameter of the connecting cable used, an adaptation sleeve having a
corresponding diameter can be inserted into the introduction opening of
the connecting cage. In order to fix the adaptation sleeve in place in
the introduction opening of the connecting cage, it can be provided that
the adaptation sleeve has a passage bore for one of the clamping screws
of the connecting cage. In this embodiment, the connecting cable and the
connecting sleeve are fixed in place with the same clamping screw.

[0021]As was explained above, so-called angled banana plugs have proven
themselves. It is practical if the electrical plug connector according to
the invention is configured accordingly, in such a manner that the base
body has a section angled transverse to its longitudinal axis, which
section forms the connecting cage. The angle between the longitudinal
axis of the base body and the longitudinal axis of the connecting cage
advantageously lies between 30° and 90°. The base body of
the electrical plug connector can be configured in multiple parts,
specifically in such a manner that the section that forms the connecting
cage can be removed. The removable section can be engaged into the base
body by way of suitable catch crosspieces, for example. It can be
practical to configure the connecting cage to be interchangeable, for
example in order to adapt the plug connector to different types of
connecting cables. It is also possible to use connecting cages of
different colors, for example for the purpose of marking the polarity
(for example red for the plus pole, black for the minus pole).

[0022]According to a further development of the electrical plug connector
according to the invention, a security pin that runs parallel to the
contact pin is formed onto the base body, which pin prevents the contact
pin from being inserted into a power outlet. If one attempts to insert
the banana plug according to the invention into an opening of a power
outlet, then the front end of the security pin comes up against the
housing of the power outlet and prevents insertion. When the banana plug
is inserted into a corresponding installation jack on the housing of a
loudspeaker or an amplifier of a hi-fi system, the security pin is not in
the way, since the installation jacks of hi-fi systems usually project so
far out of the housing that the security pin does not make contact with
the housing.

[0023]Exemplary embodiments of the invention will be described in greater
detail in the following, using the drawings. These show:

[0024]FIG. 1 side view of an angled banana plug according to the
invention;

[0027]FIG. 4 developed view of the contact pin of the angled banana plug;

[0028]FIG. 5 top view of the contact pin;

[0029]FIG. 6 spreader sleeve;

[0030]FIG. 7 first exemplary embodiment of the angled banana plug with
spreader body;

[0031]FIG. 8 second exemplary embodiment of the angled banana plug with
spreader body.

[0032]In the drawings, the electrical plug connector according to the
invention, which is an angled banana plug, is designated as a whole with
the reference number 1. The plug comprises a base body 2 as well as a
contact pin 3 disposed on the front side of the base body 2. The base
body 2 has a connecting cage 4 for accommodating a connecting cable, not
shown in any detail in the drawings, and for producing an electrically
conductive connection with the contact pin 3. As can be seen in the
developed view according to FIG. 4, the contact pin 3 consists of a total
of three contact segments 5, which are connected with one another at the
front end of the contact pin. The region designated with the reference
number 6 in FIG. 4 forms the tip of the contact pin 3 after bending
technology deformation. One of the contact segments 5, namely that
contact segment 5 that is shown on the left in FIG. 4, is configured to
be extended in length as compared with the other contact segments 5, and
has a connecting surface 7 for the connecting cable on its end side.
After bending technology deformation, the functional shape shown in FIG.
5 is obtained. The extended contact segment 5 is partially embedded in
the base body 2, which consists of plastic, as shown in FIG. 2, and
extends into the interior of the connecting cage 4. The extended contact
segment 5 lies against the inside wall of the connecting cage 4 in the
interior of the connecting cage 4. The connecting cable can be pressed
against the connecting surface 7 by means of a clamping screw 8, in order
to produce the electrical contact with the contact pin 3. In the
drawings, two clamping screws 8 are shown. The upper of the two clamping
screws serves for production of the electrical contact. The lower
clamping screw 8 is provided for fixing the mantling of the connecting
cable in place in the connecting cage. Both clamping screws 8 are guided
in a metallic threaded plate 9, which is inserted into the base body 2 in
the region of the connecting cage 4. At the lower end, the connecting
cage 4 has an introduction opening for the connecting cable. The two
clamping screws 8 can be screwed in transverse to the introduction
direction of the connecting cable. An adaptation sleeve 10 can be
inserted into the introduction opening of the connecting cage 4. The
inside diameter of the adaptation sleeve 10 essentially corresponds to
the outside diameter of the mantle of the connecting cable and thus
serves for strain relief. As shown in FIG. 2, the adaptation sleeve has a
passage bore for the lower one of the two clamping screws 8. The clamping
screw thus fulfills a dual function. It fixes the adaptation sleeve in
place in the introduction opening of the connecting cage 4, and at the
same time, it fixes the connecting cable in place on the plug 1. A
spreader pin 11a, 11b can be screwed into the base body from its back.
The spreader pin is configured to narrow conically at its front end. The
front end of the spreader pin 11a, 11b extends into the contact pin 3, as
shown in FIG. 2. The contact pin 3 can be widened radially by screwing in
the spreader pin 11a, 11b. The spreader pin consists of a metallic
spindle 11a and a handle part 11b made of plastic. The spindle 11a is
embedded in the plastic material of the handle part 11b. An outside
thread 12 is formed onto the handle part 11b, which thread is guided in a
corresponding inside thread of the base body 3. A slit spreader sleeve 13
made of spring-elastic material, for example from spring bronze, is
disposed in the interior of the contact pin 3, whereby the front end of
the spreader pin 11a, 11b, which narrows conically, moves into the
spreader sleeve 13 when it is screwed in, and widens the latter in doing
so. FIG. 2 shows the electrical plug connector according to the invention
in the unbraced position, in which the spindle 11a of the spreader pin is
only within the spreader sleeve with the front tip. In FIG. 2, it can be
seen that the spreader sleeve 13 has an inside diameter that is clearly
smaller than the outside diameter of the spindle 11a in the region of its
shaft. When the spreader pin 11a, 11b is screwed in, the spreader sleeve
is widened in accordance with the conical shape of the tip of the spindle
11a. In this connection, the spreader sleeve transfers a force that is
directed radially outward to the contact segments 5 of the contact pin 3.
This force acts as a press-down force when the outside surface of the
contact pin 3 is pressed against the inside surface of a related jack
(not shown in any detail in the drawing). Furthermore, a latch 14 that
can be releasably connected with the base body 2 is provided. The latch
14 has a locking projection 15 that engages into a circumferential groove
16 (FIG. 3) applied to the handle part 11b of the spreader pin. The latch
14 thus prevents the spreader pin 11a, 11b from being screwed too far out
of the base body 2. As can be seen in the figures, the section of the
base body that is angled away relative to the longitudinal axis of the
base body 2 and forms the connecting cage 4 can be removed. Engagement
crosspieces 17 serve to lock the connecting cage 4 onto the base body.
Finally, the figures show a security pin 18 formed onto the base body 2,
which prevents the contact pin 3 from being plugged into a power outlet.

[0033]In FIGS. 7 and 8, an elastically deformable spreader body 19 that
stands under radial bias is disposed in the interior of the contact pin,
which body widens the contact pin 3 radially and elastically. In place of
the spreader pin 11a, 11b, the spreader body 19 ensures a good electrical
connection in that the outside contact surface of the contact pin 3 is
pressed against the inside contact surface of the corresponding jack by
means of radial widening of the contact pin 3, and when this happens, the
outside diameter of the deformable contact pin 3 is automatically adapted
precisely to the inside diameter of the jack. Practically any desired
configuration and materials can be selected for the elastic spreader body
19, since the electrical properties of the plug connector are not or only
slightly influenced by the properties of the spreader body 19. In order
to keep the metal proportion of the plug connector as low as possible,
non-metallic materials, such as elastic plastics (rubber) can also be
used for the spreader body 19. In the exemplary embodiment in FIG. 7, the
spreader body 19 is an elongated plastic body having a cylindrical
outside contour and rounded-off face surfaces. In the event of radial
compression, the material of the spreader body 19 can escape in the axial
direction of the contact pin 3. In the exemplary embodiment shown in FIG.
8, the spreader body 19 is a biased cylindrical spiral spring made of
metal. The important thing is to coordinate the elasticity of the
spreader body 19 and its bias in such a manner that the friction forces
during insertion into the jack do not become too great, whereby at the
same time, the quality of the electrical contact is not allowed to
suffer.